The present invention relates to an optical disk replay device which reads in and replays data recorded on an optical disk such as a DVD or the like, and, more particularly, relates to such an optical disk replay device which can utilize a digital amp for the output of voice.
As prior art, an optical disk replay device (hereinafter simply termed a “replay device”) which replays audio files and video files recorded upon an optical disk such as a DVD or the like is nowadays in general use. Furthermore, a replay device has also been proposed which can utilize a digital amp for the output of audio, in order to replay the audio at high quality. A digital amp, as is per se well known, is an amp which, based upon inputted audio data, drives a speaker by controlling the switching ON and OFF of a switching element. Furthermore, an optical disk device which incorporates a digital amp has already been proposed.
In such a digital amp, in order to control the switching ON and OFF of the switching element based upon the audio data which is being inputted, a clock signal is required which has the same frequency as the sampling frequency of this audio data. However, the sampling frequency of the audio data which is being inputted to the digital amp is not constant. For this reason there are provided, in a typical digital amp, a detection unit which detects the sampling frequency of the audio data which is being inputted, and a signal generation unit which changes the frequency of a clock signal which it outputs, according to the sampling frequency of the audio data as detected by the detection unit.
In such a digital amp, when the sampling frequency of the audio data which is being inputted has changed, this changed sampling frequency of the audio data is detected by the detection unit, and a certain time period (around 1 to 2 seconds) is typically required until a clock signal of the sampling frequency which has thus been detected is outputted from the signal generation unit. During the interval until a clock signal of the same frequency as the sampling frequency of the audio data which has changed is outputted from the signal generation unit, the operation of the digital amp becomes unstable, and, during this interval, the audio is sometimes interrupted. Methods for eliminating this interruption of the audio are proposed in Japanese Laid-Open Patent Publication 2002-344561 and Japanese Laid-Open Patent Publication 2004-23216.
To explain Japanese Laid-Open Patent Publication 2002-344561 in simple terms, the audio data which is being inputted (i.e., the audio data before change thereof) is stored in a first buffer, and the audio data which is stored in this first buffer is processed using a clock signal of the same frequency as the sampling frequency of this audio data, with the resulting audio being outputted. When it is detected that the sampling frequency of the audio data has changed, the audio data after this change is stored in a second buffer. Thereafter, when all of the audio data which is stored in the first buffer (i.e., all of the audio data before the change of sampling frequency) has been processed, the frequency of the clock signal is changed over to the sampling frequency of the audio data which is stored in the second buffer, and subsequently the audio data which is stored in the second buffer is processed.
To explain Japanese Laid-Open Patent Publication 2004-23216 in simple terms, for a fixed time period, while the device which is inputting the audio data is being changed over, “mute” is applied so as to stop the output of audio, and the audio data which has been inputted is replayed after a delay of just this time period that “mute” has been applied. Furthermore, during the interval while this “mute” is being applied, the frequency of the clock signal is changed over to the new sampling frequency of the audio data which is being inputted.
However, with the device proposed in Japanese Laid-Open Patent Publication 2002-344561, two buffers must be provided for storing the audio data. Furthermore, a microcomputer of high processing speed and of high performance must be provided, in order to change over at high speed the buffer in which the audio data which is being inputted is stored, when it has been detected that the sampling frequency of the audio data which is being inputted has changed. Due to this, the problem has arisen of increase in the cost of the basic unit.
It should be understood that although, in Japanese Laid-Open Patent Publication 2002-344561, a structure is also described in which only one buffer needs to be provided for the storage of the audio data which is being inputted, this is a device for reducing the amount of audio data which is lost (i.e. the amount of audio data which is not replayed) when the sampling frequency of the audio data has changed, rather than being a device which is capable of preventing audio interruptions.
Furthermore, the device proposed in Japanese Laid-Open Patent Publication 2004-23216 is one which is based upon the concept that the sampling frequency of the audio data which is being inputted changes, when the device which is inputting the audio data is changed over. However, with DVD-AUDIO, the sampling frequency of the audio data is not fixed, but is sometimes different between the different tracks (i.e. between different songs). Furthermore, with DVD-VIDEO, the sampling frequency of the audio data is not fixed, but sometimes is different between the different chapters and titles. Accordingly, with the device proposed in Japanese Laid-Open Patent Publication 2004-23216, during the replay of a DVD in which the sampling frequency of the recorded audio data is not uniform, if the sampling frequency of the audio data which is being inputted changes, it is not possible to eliminate interruption of the audio after such change of the sampling frequency.
It should be understood that both Japanese Laid-Open Patent Publication 2002-344561 and Japanese Laid-Open Patent Publication 2004-23216 are proposals for a digital amp.
The objective of this invention is to provide an optical disk replay device with which interruption of the audio, when the sampling frequency of the audio data which is recorded upon an optical disk such as a DVD or the like changes, is eliminated, and moreover with which no increase in cost of the basic unit is entailed.